Workpiece clamping system

ABSTRACT

A workpiece indexing and clamping system for machining the workpiece. Spherical or narrow cylindrical heads of index pins extend from holes in a base plate into workpiece holes to align and index the workpiece. The pin portions in the base plate holes can be expanded to lock them to the base plate. Each pin has relief flats parallel to the pin axis. Clamps engage workpiece edges with thread-like angled grooves on a cam surface to force workpiece edges against the base plate during machining of the workpiece. A central clamp has a pin extending from the base plate into a workpiece hole. Angled grooves in a cam surface are brought into contact with the hole sides to force the workpiece toward the base plate and hold the central area in place during machining.

This is a divisional of copending application Ser. No. 08/613,808 filedon Mar. 6, 1996.

BACKGROUND OF THE INVENTION

This invention relates in general to the clamping of workpieces to asurface and, more specifically, to a system for indexing and clamping aworkpiece to a base plate that leaves the opposite surface free formachining or the like.

When raw material or preforms are to be machined it is necessary thatthe workpiece be tightly clamped to a base plate or an intermediatesub-plate to hold the workpiece stable at a precise position whileresisting the forces on the workpiece produced by the machiningoperation. Typically, such machining includes drilling, boring, honing,grinding and milling.

In numerical controlled machining, a machine tool, such as a millinghead, is programmed to follow a very precise path. The workpiece must belocated extremely precisely relative to certain machine datum pointsand/or datum planes from which the machining path is related ormeasured.

A number of different indexing and clamping systems have been developedto permit a workpiece to be positioned at a specific location on thesupport plate. Generally, the clamps have fingers and straps or othermeans that extend over the side of the workpiece opposite the supportingsurface. While generally effective, these upper surface clamps must becarefully positioned to avoid interference with the movement of themachine tool, such as a milling head, across the workpiece.

Insufficient clamping pressure, or the use of too few clamps, may allowthe workpiece to shift during machining, resulting in wasted,out-of-tolerance products. Further, errors in clamp placement may allowthe machine tool cutter to run against the tool, resulting in damagedclamps and serious damage to the machining tool and/or to the machineitself and could be a safety hazard to nearby personnel.

A wide, generally flat workpiece that is clamped to a support platearound the edges may lift slightly at the center due to machiningforces. Thus, the central dimensions of the product may be thinner andout-of-tolerance.

It is absolutely essential, especially with numerical controlledmachining, that the workpiece be positioned precisely relative to datumpoints or planes on the support plate. Failure to establish and maintainthe precise workpiece position will result in an improperly machined andrejected part.

A variety of components have been used to accurately locate workpieces.Among these are index pins mounted on or in the support plate andextending into precisely located holes in the workpiece. Round pinsinserted into round workpiece holes may have problems such as lack ofthe necessary concentricity, a hole that has an axis that is slightlyoff the pin axis (angularly or otherwise), pins that tend to interfereor be loose in productions holes with variable diameters, etc. Theseproblems, and others, largely keep full round index pins from having thenecessary overall accuracy and flexibility.

Thus, there is a continuing need for improved indexing and clampingsystems for workpieces to be machined, systems that have improvedreliability, accuracy and versatility and do not extend over or obstructthe workpiece surface being machined, generally the surface opposite thesurface in contact with a support or base plate.

SUMMARY OF THE INVENTION

The above-mentioned problems, and others, are overcome in accordancewith this invention by an improved workpiece clamping and locatingsystem for use in machining, in particular numerical control machining.The clamping system basically includes index pins for locating aworkpiece on a base plate, and edge clamping arrangement and a centralclamping pin. These components cooperate to provide an optimum system,although each could be used independently. The edge clamping portionbasically includes a plurality of clamps, each having a simple clamp armpivotally mounted on a support block that can be fastened to a baseplate and preferably is longitudinally movable or adjustable on top ofthe base plate surface toward and away from a side of a workpiecesupported on the base plate. Each clamp arm has a cam surface adjacentto the axis of rotation with the cam surface configured to move towardsand away from an adjacent workpiece side as the arm is pivoted. Theclamp arm includes means for pivoting the arm about the axis, preferablyan extended handle for manual pivoting or a powered gear segmentengageable with a powered drive for exact automatic movement toward andagainst the workpiece.

A workpiece is precisely positioned on a base plate by one or more (ifnecessary) index pins fastened to the base plate. Each index pin has agenerally spherical head with at least two radially spaced flats on thehead, the flats lying generally perpendicular to the base plate when theindex pin is installed on the base plate. The workpiece is positioned bylowering holes in the workpiece over correspondingly sized index pinheads. The index pins preferably have 2-4 spaced flats. In an optimumembodiment, two pairs of contiguous flats are provided, with the pairson opposite sides of the head, so that the head has a generally diamondshaped plan view.

As an aid in remotely clamping a workpiece, a central index clamping pinis preferably provided. An eccentric, at least partially threaded, headis secured through a mounting means such as a threaded extension to abase plate. The vertical axis of the partially threaded head is offsetfrom the vertical axis of the mounting means or main body to provideeccentric motion of the head when the clamping pin is rotated. Theclamping pin is rotatable through an aperture in the top of the headopposite to the pin mounting means which receives a tool, such as anAllen wrench, screwdriver or the like. When a workpiece hole is placedover the clamping pin (or the clamping pin is inserted through theworkpiece into the base plate) and the pin is rotated (counter-clockwisefor a right-hand thread) the threads will frictionally engage a side ofthe hole and force the workpiece tightly sideways and down against thebase plate. This arrangement is particularly useful with wide, thinworkpieces where, in the absence of central clamping action, a millingtool or the like is likely to cause the workpiece central area to liftand be incorrectly machined and/or cause the workpiece center tovibrate, thus causing negative, unwanted results.

Any suitable base plate may be used with the clamping system of thisinvention. Where the workpiece is relatively thick, the workpiece may beinstalled directly onto the surface of a single sheet base plate. Wherethe workpiece is relatively thin, upper and lower base plates may beused, with a wide lower base plate and a smaller upper baseplate,typically matching the outline of the workpiece and having a surfaceequal to or slightly larger than that of the workpiece.

Depending on the size of the workpiece, at least two index pins and oneor more central clamp pins may be used with the edge clamping system.

BRIEF DESCRIPTION OF THE DRAWING

Details of the invention, and of preferred embodiments thereof, will befurther understood upon reference to the drawing, wherein:

FIG. 1 is a plan view of the clamping system, here including four edgeclamps and a central clamp and several kinds of index pins;

FIG. 2 is a section view taken on line 2--2 in FIG. 1;

FIG. 3 is a detail perspective view of one index pin embodiment;

FIG. 4 is a plan view of the pin shown in FIG. 3;

FIG. 5 is a section view taken on line 5--5 in FIG. 4;

FIG. 6 is a view of the lower end of the pin shown in FIG. 3;

FIG. 7 is a perspective view, partially cut-away, of one combinationcentral index/clamping pin;

FIG. 8 is a detail perspective view of one edge clamp arm;

FIG. 9 is an plan view of another locating pin embodiment; and

FIG. 10 is a side elevation view of the pin of FIG. 9.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIG. 1, there is seen a base plate assembly 10 made up of alower plate 12 and an upper plate 14. A workpiece 16 to be machined isinstalled on upper plate 14.

Four edge clamp assemblies 18, as seen in FIGS. 1 and 8, are located onopposite sides of workpiece 16. Depending on the size, complexity andparticular machining operations to be accomplished, from two to a largernumber of clamp assemblies 18 may be used in various clamp sizes.

Each clamp assembly 18 includes a support block 20 secured to lowerplate 12 by cap screws 22. Cap screws 22 are near the ends of slot 21 insupport block. The spaced arrangement provides maximum strength, withsome range of adjustment of the position of support block 20 toward andaway from workpiece 16. An arm 24 is mounted on each support block 20 bya shoulder screw 26 that permits the arm to pivot about an axis centeredon screw 26. Each arm 24 has a cam surface 28 around each axis with acontinuous varying diameter. When an arm 24 is moved in the directionindicated by arrow 30, the cam diameter increases, increasing clampingpressure on the edge of workpiece 16. In three of the arms 24 shown, anextended handle 32 is provide with which the arm is manually movedbetween clamped and unclamped positions. The other arm 24, seen to thelower right in FIG. 1, shows an alternate embodiment where, in place ofhandle 32, a gear segment 34 is provided that engages a gear in a powerdrive 36, typically a small electrical gear motor, to automatically movethe upper portion of arm 24 between clamped and unclamped positions.

As seen in FIGS. 1, 2 and 5, grooves 37 similar to screw threads areprovided along cam surface 28. Preferably, the cam surface 28 and powerdrive surface 34 are suitably hardened or heat treated for strength anddurability. Grooves preferably have sharp apexes and are slanted so thatas the grooves engage and move along the edge of workpiece 16 thegrooves force the workpiece tightly down against upper plate 14, as wellas horizontally in two additional directions against opposing indexpins, bars and the like and other opposing clamps as shown in FIGS. 1and 2. Since clamp assemblies 18 do not extend above the upper surfaceof workpiece 16, machining tools, such as mills, can traverse the entireupper surface without interference from, or impact against, clamps aswould be the case with conventional clamping systems.

Generally, workpiece 16 must be precisely located on base plate 10 toalign with the machining tools, especially in the case of NumericalControl (N/C) machining. As seen in FIGS. 1 and 3, a novel and moreeffective index pin system is provided to correctly locate theworkpiece.

Three types of ball index pins are shown, a diamond-shaped ball pin 38,a triangular-shaped ball pin 40 and a square-shaped ball pin 42. Each ofthese pins is secured to upper base plate 14 and slip fits precisely ina hole 44 of suitable diameter, precisely located in the workpiece.Thus, workpiece 16 is exactly located relative to the pins formachining. Each type of ball pin may be used in conjunction with otherconventional pins and locators, with particular pin types selected tomeet specific conditions and needs.

The diamond ball pin 38 embodiment is shown in perspective in FIG. 3 andin orthographic view in FIGS. 4, 5 and 6. The upper portion 39 of eachof the pins 38, 40 and 42 is basically spherical before final machiningof flats on the sides. Each pin has a head of different configuration ona base flange 46 and extension 48 for insertion into a correspondinglyslip fit hole 47 in upper plate 14. Each pin has the desired number offlats 50 machined into the spherical surface 49 along planes parallel tothe vertical axis of the pin, ultimately perpendicular to the surface ofupper plate 14. Diamond ball pin 38 has two pairs of contiguous flats49, arranged on opposite sides of the pin to provide a diamond-likeappearance in a plan view. Thus, the two opposed remaining sphericalsurfaces 50 are the only "tangent line" portions of the pin that contactthe interior of a hole 44, providing accurate positioning in two opposeddirections, at desired minimum contact, while providing exceptionalrelief in the remaining directions, thus guaranteeing absolute minimumhole and pin interference. Similarly, triangular pin 40 has threeequally spaced flats 49, providing three equally spaced sphericalsurfaces 50 and square pin 42 has four equally spaced flats 49 and fourequally spaced spherical surfaces 50. Pins 40 and 42 are designed toreplace existing full size pins for more accurate indexing and alignmentwith minimum interference. The diamond ball pin configuration isconsidered optimum, and equally spaced spherical surfaces 50 arepreferred for most versatile indexing ability, especially when severalplanes are involved at complex or compound angles toward each other.

If desired, the surfaces 50 could be rounded to provide essentially aline contact with a workpiece. Further, if desired a different number offlats could be provided, spaced apart other than equally. Clearadvantages of pins 38, 40 and 42 include precise yet simple and quickindex capability in complex set-ups with additional tolerance benefits.Preferably the ball pins 38, 40 and 42 are suitably hardened or heattreated and otherwise processed for strength, durability and longevity.

For installing and removing pins 38, 40 and 42, an aperture 54 isprovided in the upper end to receive a tool, such as a screwdriver,Allen wrench or the like to rotate a setscrew 52 threaded into a narrowlower portion of aperture 54. The interior of aperture 54 bears threads53, which taper to a narrower lower end of aperture 54. Extension 48 hastwo or four axial slots 55. Thus, as setscrew 52 is threaded downwardly,extension 48 between slots 55 is forced outwardly to engage the interiorwall of hole 47. Since the pin extension 48 is a slip fit in hole 47, anexpansion of extension 48 of only 0.001 to 0.003 inch is generallysufficient to hold the pin securely in the hole. The pin is easilyremoved by simply inserting an Allen wrench into a hexagonal hole insetscrew 52 or a screwdriver into a corresponding slot in the setscrewto move the setscrew back up threads 53.

Two flats 57 are preferably included on opposite sides of flange 46 sothat the head can be held in the proper orientation with a conventionalwrench while the setscrew is being tightened.

Large, thin, or flat workpieces 16 often tend to lift at central areasduring milling. A central clamp 58 as shown in FIGS. 1 and 7 ispreferably used. Central clamp 58 basically comprises a threadedextension 60 on which a cylindrical, coaxial, base or locator section 63is secured, with a cylindrical head 62 mounted on the base 63, with theaxis of extension 60 and base or locator section 63 offset from the axisof head 62. The offset head 62 is sufficiently eccentric to provide acam action of the head when rotated about the axis of threaded extension60 and base 63. Locator section 63 is a close slip fit with hole 65 inplate 14 to assure precise location. Central clamp 58 is threaded intoupper plate 14, but not tight against upper plate 14.

Workpiece 16 has a hole 64 that fits over central clamp 58 and is sizedso that as the clamp is rotated by means of a conventional Allen wrenchor the like engaging hexagonal opening 68 in head 62 the cam head 62moves into engagement with the wall of hole 64 when rotated in onedirection and out of engagement when rotated in the opposite direction.In order to provide the clamping action, forcing workpiece 16 againstupper plate 14, angled grooves, preferably conventional threads 66,either right-handed or left-handed, as desired, are provided on theouter cam surface of head 62. Thus, when the cam surface is rotated intopressure contact with the wall of hole 64, threads 66 will engage thewall and drive the workpiece 16 against upper plate 14 in the samemanner as the grooves 37 on clamp arm 24. Preferably, central clamp pin58 is suitably hardened, heat treated or otherwise processed forstrength, durability and longevity. If desired, a threaded bushing couldbe used in lower plate 12 rather than directly threading the lower plateopening and a guide bushing could be provided in the opening in upperplate 14 to surround the locator section 63.

A tool receiving opening 68 is provided in the end of head 62 to permitcentral clamp 58 to be rotated in the manner described by any suitabletool, such as an Allen wrench, screwdriver or the like.

Another embodiment of a locator pin suitable for use with the overallsystem of this invention is illustrated in FIGS. 9 and 10. In this case,base 46, extension 48, slot(s) 55 and expansion setscrew 52 are the sameas discussed above in conjunction with FIGS. 3-6. In this embodiment,however, upper portion 72 is initially machined as a cylinder ratherthan as a sphere, then is machined to provide a narrow cylindrical band.Finally, two or more flats 74 are machined to provide a diamond shaped,square, triangle, or other desired configuration, as discussed above.

A flange 46 is provided between said upper portion 72 and extension 48to engage the base plate surface when the pin is in place thereon. Twoflats 57 may be provided on opposite sides of flange 46 to be engaged bya conventional wrench while the central setscrew is moved.

This embodiment is particularly suitable where the locating hole 44 inwhich the pin is inserted is parallel to the pin axis, yet minimum indexcontact is guaranteed with minimum interference. Where the pin axis andhole may be at an angle to each others, the spherical upper portionembodiments are preferred, since this makes a complex set-up simple andeasy to work with, at minimum cost.

While a flat workpiece 16 has been illustrated for convenience ofschematic illustration, workpiece could have any suitable shape,including shapes having high peripheral areas (such as an open box-likeshape) which are particularly difficult to clamp with prior clampingsystems.

While certain specific relationships, materials and other parametershave been detailed in the above description of preferred embodiments,those can be varied, where suitable, with similar results. Otherapplications, variations and ramifications of the present invention willoccur to those skilled in the art upon reading the present disclosure.Those are intended to be included within the scope of this invention asdefined in the appended claims.

I claim:
 1. An index pin for fastening to a baseplate and extending intoa workpiece hole for locating a workpiece relative to a baseplate whichcomprises:a head; least two flats on said head; means for fastening saidhead to a base plate with said flats aligned substantially perpendicularto said base plate; a coaxial extension having a proximal end secured tosaid head, a distal end extending opposite said proximal end and havinga predetermined diameter for fitting into a base plate hole; an axialaperture through said head and extension; said axial aperture having aninternal thread; at least one slot in the extension distal end; saidaxial aperture having a gradually decreasing diameter toward said distalend; and a setscrew threaded into said internal thread:whereby threadingsaid setscrew toward said distal end will expand said extension intopressure contact with said base plate hole.
 2. The index pin accordingto claim 1 wherein three flats are provided, evenly spaced apart aroundsaid head.
 3. The index pin according to claim 1 wherein four flats areprovided, evenly spaced apart around said head.
 4. The index pinaccording to claim 1 wherein two opposed spaced pairs of contiguousflats are provided around said head, whereby said index pin is generallydiamond-shaped in plan view.
 5. The index pin according to claim 1wherein said head is generally spherical.
 6. The index pin according toclaim 1 wherein said head has an axially narrow generally cylindricalsurface.
 7. An index pin for fastening to a baseplate and extending intoa workpiece hole for locating a workpiece relative to a baseplate whichcomprises:a generally spherical head; two opposed spaced pairs ofcontiguous flats on said head so that said index pin is generallydiamond-shaped in plan view; means for fastening said head to a baseplate with said flats aligned substantially perpendicular to said baseplate; a coaxial extension having a proximal end secured to said headand having a predetermined diameter for fitting into a base plate hole;an axial aperture through said head and extension; said axial aperturehaving an internal thread; at least one slot in the extension distalend; said axial aperture having a gradually decreasing diameter towardsaid distal end; and a setscrew threaded into said internalthread:whereby threading said setscrew toward said distal end willexpand said extension into pressure contact with said base plate hole.8. An index pin for fastening to a baseplate and extending into aworkpiece hole for locating a workpiece relative to a baseplate whichcomprises:a generally cylindrical head; two opposed spaced pairs ofcontiguous flats on said head so that said index pin is generallydiamond-shaped in plan view; means for fastening said head to a baseplate with said flats aligned substantially perpendicular to said baseplate; a coaxial extension having a proximal end secured to said headand having a predetermined diameter for fitting into a base plate hole;an axial aperture through said head and extension; said axial aperturehaving an internal thread; at least one slot in the extension distalend; said axial aperture having a gradually decreasing diameter towardsaid distal end; and a setscrew threaded into said internalthread:whereby threading said setscrew toward said distal end willexpand said extension into pressure contact with said base plate hole.